diff --git a/CHANGELOG.md b/CHANGELOG.md
index 438117e69..5e185cc30 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,12 @@
 # UNRELEASED
 
+## Deprecations
+* The `Sourceable` field has been deprecated on `RunTrigger`. Instead, use `SourceableChoice` to locate the non-empty field representing the actual sourceable value by @brandonc [#816](https://github.com/hashicorp/go-tfe/pull/816)
+
+## Features
+* Adds `LockedBy` relationship field to `Workspace` by @brandonc [#816](https://github.com/hashicorp/go-tfe/pull/816)
+* Adds `CreatedBy` relationship field to `TeamToken`, `UserToken`, and `OrganizationToken` by @brandonc [#816](https://github.com/hashicorp/go-tfe/pull/816)
+
 # v1.40.0
 
 ## Bug Fixes
@@ -9,7 +16,7 @@
 * Add organization scope field for oauth clients by @Netra2104 [#812](https://github.com/hashicorp/go-tfe/pull/812)
 * Added BETA support for including `projects` relationship to oauth_client on create by @Netra2104 [#806](https://github.com/hashicorp/go-tfe/pull/806)
 * Added BETA method `AddProjects` and `RemoveProjects` for attaching/detaching oauth_client to projects by Netra2104 [#806](https://github.com/hashicorp/go-tfe/pull/806)
-* Adds a missing interface `WorkspaceResources` and the `List` method by @stefan-kiss [Issue#754](https://github.com/hashicorp/go-tfe/issues/754) 
+* Adds a missing interface `WorkspaceResources` and the `List` method by @stefan-kiss [Issue#754](https://github.com/hashicorp/go-tfe/issues/754)
 
 # v1.39.2
 
diff --git a/go.mod b/go.mod
index a5817af04..3101d24c7 100644
--- a/go.mod
+++ b/go.mod
@@ -10,7 +10,7 @@ require (
 	github.com/hashicorp/go-slug v0.13.2
 	github.com/hashicorp/go-uuid v1.0.3
 	github.com/hashicorp/go-version v1.6.0
-	github.com/hashicorp/jsonapi v0.0.0-20210826224640-ee7dae0fb22d
+	github.com/hashicorp/jsonapi v1.2.0
 	github.com/stretchr/testify v1.8.4
 	golang.org/x/sync v0.5.0
 	golang.org/x/time v0.4.0
diff --git a/go.sum b/go.sum
index bb47f6fce..a61b158d0 100644
--- a/go.sum
+++ b/go.sum
@@ -18,8 +18,8 @@ github.com/hashicorp/go-uuid v1.0.3 h1:2gKiV6YVmrJ1i2CKKa9obLvRieoRGviZFL26PcT/C
 github.com/hashicorp/go-uuid v1.0.3/go.mod h1:6SBZvOh/SIDV7/2o3Jml5SYk/TvGqwFJ/bN7x4byOro=
 github.com/hashicorp/go-version v1.6.0 h1:feTTfFNnjP967rlCxM/I9g701jU+RN74YKx2mOkIeek=
 github.com/hashicorp/go-version v1.6.0/go.mod h1:fltr4n8CU8Ke44wwGCBoEymUuxUHl09ZGVZPK5anwXA=
-github.com/hashicorp/jsonapi v0.0.0-20210826224640-ee7dae0fb22d h1:9ARUJJ1VVynB176G1HCwleORqCaXm/Vx0uUi0dL26I0=
-github.com/hashicorp/jsonapi v0.0.0-20210826224640-ee7dae0fb22d/go.mod h1:Yog5+CPEM3c99L1CL2CFCYoSzgWm5vTU58idbRUaLik=
+github.com/hashicorp/jsonapi v1.2.0 h1:ezDCzOFsKTL+KxVQuA1rNxkIGTvZph1rNu8kT5A8trI=
+github.com/hashicorp/jsonapi v1.2.0/go.mod h1:Yog5+CPEM3c99L1CL2CFCYoSzgWm5vTU58idbRUaLik=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
diff --git a/helper_test.go b/helper_test.go
index 4a731aaf2..4508213c4 100644
--- a/helper_test.go
+++ b/helper_test.go
@@ -22,6 +22,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"reflect"
 	"runtime"
 	"strings"
 	"testing"
@@ -2851,6 +2852,53 @@ func betaFeaturesEnabled() bool {
 	return os.Getenv("ENABLE_BETA") == "1"
 }
 
+// isEmpty gets whether the specified object is considered empty or not.
+func isEmpty(object interface{}) bool {
+	// get nil case out of the way
+	if object == nil {
+		return true
+	}
+
+	objValue := reflect.ValueOf(object)
+
+	switch objValue.Kind() {
+	// collection types are empty when they have no element
+	case reflect.Chan, reflect.Map, reflect.Slice:
+		return objValue.Len() == 0
+	// pointers are empty if nil or if the value they point to is empty
+	case reflect.Ptr:
+		if objValue.IsNil() {
+			return true
+		}
+		deref := objValue.Elem().Interface()
+		return isEmpty(deref)
+	// for all other types, compare against the zero value
+	// array types are empty when they match their zero-initialized state
+	default:
+		zero := reflect.Zero(objValue.Type())
+		return reflect.DeepEqual(object, zero.Interface())
+	}
+}
+
+// requireExactlyOneNotEmpty accepts any number of values and calls t.Fatal if
+// less or more than one is empty.
+func requireExactlyOneNotEmpty(t *testing.T, v ...any) {
+	if len(v) == 0 {
+		t.Fatal("Expected some values for requireExactlyOneNotEmpty, but received none")
+	}
+
+	empty := 0
+	for _, value := range v {
+		if isEmpty(value) {
+			empty += 1
+		}
+	}
+
+	if empty != len(v)-1 {
+		t.Fatalf("Expected exactly one value to not be empty, but found %d empty values", empty)
+	}
+}
+
 // Useless key but enough to pass validation in the API
 const testGpgArmor string = `
 -----BEGIN PGP PUBLIC KEY BLOCK-----
diff --git a/organization_token.go b/organization_token.go
index 2058f4695..68dd02c25 100644
--- a/organization_token.go
+++ b/organization_token.go
@@ -39,12 +39,13 @@ type organizationTokens struct {
 
 // OrganizationToken represents a Terraform Enterprise organization token.
 type OrganizationToken struct {
-	ID          string    `jsonapi:"primary,authentication-tokens"`
-	CreatedAt   time.Time `jsonapi:"attr,created-at,iso8601"`
-	Description string    `jsonapi:"attr,description"`
-	LastUsedAt  time.Time `jsonapi:"attr,last-used-at,iso8601"`
-	Token       string    `jsonapi:"attr,token"`
-	ExpiredAt   time.Time `jsonapi:"attr,expired-at,iso8601"`
+	ID          string           `jsonapi:"primary,authentication-tokens"`
+	CreatedAt   time.Time        `jsonapi:"attr,created-at,iso8601"`
+	Description string           `jsonapi:"attr,description"`
+	LastUsedAt  time.Time        `jsonapi:"attr,last-used-at,iso8601"`
+	Token       string           `jsonapi:"attr,token"`
+	ExpiredAt   time.Time        `jsonapi:"attr,expired-at,iso8601"`
+	CreatedBy   *CreatedByChoice `jsonapi:"polyrelation,created-by"`
 }
 
 // OrganizationTokenCreateOptions contains the options for creating an organization token.
diff --git a/organization_token_integration_test.go b/organization_token_integration_test.go
index c72d1de0d..b84d8ece0 100644
--- a/organization_token_integration_test.go
+++ b/organization_token_integration_test.go
@@ -24,6 +24,7 @@ func TestOrganizationTokensCreate(t *testing.T) {
 		ot, err := client.OrganizationTokens.Create(ctx, orgTest.Name)
 		require.NoError(t, err)
 		require.NotEmpty(t, ot.Token)
+		requireExactlyOneNotEmpty(t, ot.CreatedBy.Organization, ot.CreatedBy.Team, ot.CreatedBy.User)
 		tkToken = ot.Token
 	})
 
diff --git a/run_trigger.go b/run_trigger.go
index 1f42a3e57..c12e9b964 100644
--- a/run_trigger.go
+++ b/run_trigger.go
@@ -43,17 +43,23 @@ type RunTriggerList struct {
 	Items []*RunTrigger
 }
 
+// SourceableChoice is a choice type struct that represents the possible values
+// within a polymorphic relation. If a value is available, exactly one field
+// will be non-nil.
+type SourceableChoice struct {
+	Workspace *Workspace
+}
+
 // RunTrigger represents a run trigger.
 type RunTrigger struct {
 	ID             string    `jsonapi:"primary,run-triggers"`
 	CreatedAt      time.Time `jsonapi:"attr,created-at,iso8601"`
 	SourceableName string    `jsonapi:"attr,sourceable-name"`
 	WorkspaceName  string    `jsonapi:"attr,workspace-name"`
-
-	// Relations
-	// TODO: this will eventually need to be polymorphic
-	Sourceable *Workspace `jsonapi:"relation,sourceable"`
-	Workspace  *Workspace `jsonapi:"relation,workspace"`
+	// DEPRECATED. The sourceable field is polymorphic. Use SourceableChoice instead.
+	Sourceable       *Workspace        `jsonapi:"relation,sourceable"`
+	SourceableChoice *SourceableChoice `jsonapi:"polyrelation,sourceable"`
+	Workspace        *Workspace        `jsonapi:"relation,workspace"`
 }
 
 // https://developer.hashicorp.com/terraform/cloud-docs/api-docs/run-triggers#query-parameters
diff --git a/run_trigger_integration_test.go b/run_trigger_integration_test.go
index e5630583b..a13055a13 100644
--- a/run_trigger_integration_test.go
+++ b/run_trigger_integration_test.go
@@ -129,7 +129,9 @@ func TestRunTriggerList(t *testing.T) {
 		require.NoError(t, err)
 		require.NotEmpty(t, rtl.Items)
 		require.NotNil(t, rtl.Items[0].Sourceable)
-		assert.NotEmpty(t, rtl.Items[0].Sourceable.Name)
+		assert.NotEmpty(t, rtl.Items[0].Sourceable)
+		assert.NotNil(t, rtl.Items[0].SourceableChoice.Workspace)
+		assert.NotEmpty(t, rtl.Items[0].SourceableChoice.Workspace)
 	})
 
 	t.Run("with a RunTriggerType that does not return included data", func(t *testing.T) {
diff --git a/team_token.go b/team_token.go
index 3cf636086..31c586021 100644
--- a/team_token.go
+++ b/team_token.go
@@ -39,12 +39,13 @@ type teamTokens struct {
 
 // TeamToken represents a Terraform Enterprise team token.
 type TeamToken struct {
-	ID          string    `jsonapi:"primary,authentication-tokens"`
-	CreatedAt   time.Time `jsonapi:"attr,created-at,iso8601"`
-	Description string    `jsonapi:"attr,description"`
-	LastUsedAt  time.Time `jsonapi:"attr,last-used-at,iso8601"`
-	Token       string    `jsonapi:"attr,token"`
-	ExpiredAt   time.Time `jsonapi:"attr,expired-at,iso8601"`
+	ID          string           `jsonapi:"primary,authentication-tokens"`
+	CreatedAt   time.Time        `jsonapi:"attr,created-at,iso8601"`
+	Description string           `jsonapi:"attr,description"`
+	LastUsedAt  time.Time        `jsonapi:"attr,last-used-at,iso8601"`
+	Token       string           `jsonapi:"attr,token"`
+	ExpiredAt   time.Time        `jsonapi:"attr,expired-at,iso8601"`
+	CreatedBy   *CreatedByChoice `jsonapi:"polyrelation,created-by"`
 }
 
 // TeamTokenCreateOptions contains the options for creating a team token.
diff --git a/team_token_integration_test.go b/team_token_integration_test.go
index fa8433fc9..05ca77e11 100644
--- a/team_token_integration_test.go
+++ b/team_token_integration_test.go
@@ -24,6 +24,8 @@ func TestTeamTokensCreate(t *testing.T) {
 		tt, err := client.TeamTokens.Create(ctx, tmTest.ID)
 		require.NoError(t, err)
 		require.NotEmpty(t, tt.Token)
+		require.NotEmpty(t, tt.CreatedBy)
+		requireExactlyOneNotEmpty(t, tt.CreatedBy.Organization, tt.CreatedBy.Team, tt.CreatedBy.User)
 		tmToken = tt.Token
 	})
 
diff --git a/user_token.go b/user_token.go
index 2251aae33..6672412b5 100644
--- a/user_token.go
+++ b/user_token.go
@@ -43,14 +43,24 @@ type UserTokenList struct {
 	Items []*UserToken
 }
 
+// CreatedByChoice is a choice type struct that represents the possible values
+// within a polymorphic relation. If a value is available, exactly one field
+// will be non-nil.
+type CreatedByChoice struct {
+	Organization *Organization
+	Team         *Team
+	User         *User
+}
+
 // UserToken represents a Terraform Enterprise user token.
 type UserToken struct {
-	ID          string    `jsonapi:"primary,authentication-tokens"`
-	CreatedAt   time.Time `jsonapi:"attr,created-at,iso8601"`
-	Description string    `jsonapi:"attr,description"`
-	LastUsedAt  time.Time `jsonapi:"attr,last-used-at,iso8601"`
-	Token       string    `jsonapi:"attr,token"`
-	ExpiredAt   time.Time `jsonapi:"attr,expired-at,iso8601"`
+	ID          string           `jsonapi:"primary,authentication-tokens"`
+	CreatedAt   time.Time        `jsonapi:"attr,created-at,iso8601"`
+	Description string           `jsonapi:"attr,description"`
+	LastUsedAt  time.Time        `jsonapi:"attr,last-used-at,iso8601"`
+	Token       string           `jsonapi:"attr,token"`
+	ExpiredAt   time.Time        `jsonapi:"attr,expired-at,iso8601"`
+	CreatedBy   *CreatedByChoice `jsonapi:"polyrelation,created-by"`
 }
 
 // UserTokenCreateOptions contains the options for creating a user token.
diff --git a/user_token_integration_test.go b/user_token_integration_test.go
index 09c101b84..1eb95eff6 100644
--- a/user_token_integration_test.go
+++ b/user_token_integration_test.go
@@ -6,10 +6,11 @@ package tfe
 import (
 	"context"
 	"fmt"
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
 	"testing"
 	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 // TestUserTokens_List tests listing user tokens
@@ -122,6 +123,8 @@ func TestUserTokens_Read(t *testing.T) {
 		// object. Empty that out for comparison
 		token.Token = ""
 		assert.Equal(t, token, to)
+
+		requireExactlyOneNotEmpty(t, token.CreatedBy.Organization, token.CreatedBy.Team, token.CreatedBy.User)
 	})
 }
 
diff --git a/workspace.go b/workspace.go
index 1470e5599..728db37ca 100644
--- a/workspace.go
+++ b/workspace.go
@@ -114,6 +114,15 @@ type WorkspaceList struct {
 	Items []*Workspace
 }
 
+// LockedByChoice is a choice type struct that represents the possible values
+// within a polymorphic relation. If a value is available, exactly one field
+// will be non-nil.
+type LockedByChoice struct {
+	Run  *Run
+	User *User
+	Team *Team
+}
+
 // Workspace represents a Terraform Enterprise workspace.
 type Workspace struct {
 	ID                         string                      `jsonapi:"primary,workspaces"`
@@ -164,6 +173,7 @@ type Workspace struct {
 	Project                     *Project              `jsonapi:"relation,project"`
 	Tags                        []*Tag                `jsonapi:"relation,tags"`
 	CurrentConfigurationVersion *ConfigurationVersion `jsonapi:"relation,current-configuration-version,omitempty"`
+	LockedBy                    *LockedByChoice       `jsonapi:"polyrelation,locked-by"`
 
 	// Links
 	Links map[string]interface{} `jsonapi:"links,omitempty"`
diff --git a/workspace_integration_test.go b/workspace_integration_test.go
index d100e1a98..7cb7d7583 100644
--- a/workspace_integration_test.go
+++ b/workspace_integration_test.go
@@ -1874,9 +1874,15 @@ func TestWorkspacesLock(t *testing.T) {
 	t.Cleanup(wTestCleanup)
 
 	t.Run("with valid options", func(t *testing.T) {
+		require.Empty(t, wTest.LockedBy)
+
 		w, err := client.Workspaces.Lock(ctx, wTest.ID, WorkspaceLockOptions{})
 		require.NoError(t, err)
 		assert.True(t, w.Locked)
+
+		require.NoError(t, err)
+		require.NotEmpty(t, w.LockedBy)
+		requireExactlyOneNotEmpty(t, w.LockedBy.Run, w.LockedBy.Team, w.LockedBy.User)
 	})
 
 	t.Run("when workspace is already locked", func(t *testing.T) {